Aadel Chaudhuri
Results Section for Experiment 1C--Results of Streaking from Experiment 1-B
Hypothesis: Known strains should grow predictably on Kanr selection plates, and the
appropriate indicators should be observed on Mac Ara and Lac Kan screening plates.
These indicators should allow the inference of relevant genotypes.
Results
Growth was observed on plates that met the strains' phenotypic criteria. For example,
only Kanamycin-resistant strains grew on Kanamycin-coated plates. All strains used
were however Kanamycin-resistant, so as predicted, all grew. This notwithstanding, each
plate contained different media designed to test for the presence of certain proteins, and
thus notify of certain genotypes. The observed indicator phenotypes are shown in table 1.
Based on the indicator phenotypes (i.e. color), the underlying metabolic phenotypes were
inferred. This was done by noting the properties of MacConkey medium and X-gal.
MacConkey medium causes acidic (Carbohydrate-metabolizing) cells to appear red, and
basic (amino acid-metabolizing) cells to appear white. Thus, cells capable of processing
Arabinose should appear red in MacConkey medium supplemented with Arabinose (Ara+
phenotype), while those unable to do so should appear white (Ara- phenotype). A similar
condition holds for cells capable of Lactose metabolism plated on MacConkey plates
supplemented with Lactose.
X-gal, an analogous indicator, tests the ability of Beta-galactosidase, an enzyme produced
by the cell's LacZ gene. If functioning, the enzyme cleaves X-gal, producing a blue color
in X-gal-supplemented medium (LacZ+ phenotype). Otherwise, no color is produced
(LacZ- phenotype).
Table 1 -- Observed and Inferred Strain Phenotypes
Strain
Plate Medium
Indicator Phenotype Inferred Phenotype
BK1
Mac Ara Kan
White
Ara-, Kanr
BK1
Mac Lac Kan
White
LacY-, Kanr
BK1
LB Kan
--BK1
LB Ara X-gal Kan
Blue
LacZ+, Kanr
EJ1
Mac Ara Kan
White
Ara-, Kanr
EJ1
Mac Lac Kan
White
LacY-, Kanr
EJ1
LB Kan
-Kanr
EJ1
LB Ara X-gal Kan
White
LacZ-, Kanr
H24
Mac Ara Kan
White
Ara-, Kanr
H24
Mac Lac Kan
White
LacY-, Kanr
H24
LB Kan
-Kanr
H24
LB Ara X-gal Kan
Blue
LacZ+, Kanr
JET2
Mac Ara Kan
Red
Ara+, Kanr
JET2
Mac Lac Kan
White
LacY-, Kanr
JET2
LB Kan
-Kanr
JET2
LB Ara X-gal Kan
White
LacZ-, Kanr
Observed and inferred phenotypes are shown based on each plating. Only cells that grew
on Kanamycin were considered. Plates on which no indicator phenotype was displayed
were not indicator plates.